He is already working (semi-govt job) no restrictions on social security card.
I think you misunderstood the restriction I was referring to.
For noncitizens who get a Social Security card, there will be some wording like "Not valid for employment without DHS authorization" on the card unless they had permanent resident status at the time the SS card was issued. Permanent residents who still have a SS card with that restrictive wording will have to show their green card when obtaining employment (or green card equivalent like the I-551 passport stamp).
If the SS card is issued after obtaining LPR status or citizenship, it won't have that wording. A card without that restrictive wording can be used in combination with an acceptable ID such as a driver's license as proof of employment eligibility,
without having to show the green card. So if he changes jobs, he won't need to show a valid green card if he has the unrestricted Social Security card, but of course he will need a new green card to travel internationally.
The lawyer (very experienced but very costly) wants to get him a new GC because technically the present one was not right.
If the lawyer is referring to getting new GC
status, he would have to first lose his current status (whether forcibly or voluntarily) to qualify for a fresh "untainted" GC status. Voluntarily would mean leaving the US and officially surrendering his GC at a consulate, then you can file I-130 for him to return eventually. I wouldn't advise going that route.
But if we're talking about just getting a new card, he can apply for renewal. Forcible revocation of his status is highly unlikely as a result of applying for renewal, given that they didn't attempt revocation after his naturalization attempt, and GC renewal involves less scrutiny than naturalization. And if it's indeed true that his priority date was current for married sons of USC when he got married and immigrated, that makes revocation even more unlikely or maybe impossible.